PSI - Issue 60

Vivek Srivastava et al. / Procedia Structural Integrity 60 (2024) 233–244 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

243 11

Specimen

Critical crack length, a C (mm)

Fatigue Life, N f (Cycles)

N f _ICCP / N f _FC

FC

38 43

12,40,350 30,39,357

2.45

ICCP

4. Conclusions

• XS-grade shipbuilding steel was found to exhibit higher sub-critical or threshold corrosion fatigue crack propagation resistance in ICCP condition (∆K TH_EFF = 18 MPa √m) as compared to FC condition (∆K TH_EFF = 14 MPa √m) in terms of effective values estimated after crack closure corrections. • Long-crack corrosion fatigue crack propagation resistance was found superior in ICCP condition than that in FC condition. Higher correlation coefficient (R 2 ) of ICCP specimen to that of FC specimen indicated more stable CFCGR in ICCP condition. • SEM fractography of the FC specimen revealed debonding of non-metallic inclusions and the formation of micro-pits/micro-cracks due to aggressive chloride environment as dominant damage mechanisms. • SEM fractography of ICCP-protected specimen exhibited a remarkedly contrasting morphology. A signature pattern of PSCs formation and a proportional increase in their density with increasing stress intensity levels or primary crack growth was observed. This fracture morphology indicated the phenomena of primary-crack branching and further arrest, leading to retarded crack growth rates under ICCP protection. • Fatigue life analysis also confirmed this finding, where the beneficial ICCP-protection effect resulted in at least two times enhancement in fatigue lives from the unprotected FC condition. Acknowledgements This work was carried out with administrative and financial support from Defence Research and Development Organization (DRDO) and Indian Institute of Technology (IIT) Bombay. The support is gratefully acknowledged. Abbas, M. and Shafiee, M. (2020) ‘An overview of maintenance management strategies for corroded steel structures in extreme m arine environments’, Marine Structures , 71(March 2019), p. 102718. doi: 10.1016/j.marstruc.2020.102718. Anderson, T. L. (2005) Fracture Mechanics: Fundamentals and Applications . Third. CRC Press. ASTM E647−13 (2014) ‘Standard Test Method for Measurement of Fatigue Crack Growth Rates’, American Society for Testing and Materials , pp. 1 – 50. doi: 10.1520/E0647-15E01.2. ‘ASTM Standard E8: Test Methods for Tension Testing of Metallic Materials’ (2004) in ASTM International , pp. 1 – 27. Available at: www.astm.org. ‘ASTM Standard E92 Vickers Hardness of Matallic Materials’ (1997) ASTM International , (West Conshohocken, PA, 2003), p. 10. ‘ASTM Standard G59 Test Method for Conducting Potentiodynamic Polarization Resistance Measurements’ (2003) ASTM International , (West Conshohocken, PA, 2003). doi: 10.1520/G0059-23, www.astm.org. Cabrini, M. et al. (2020) ‘Hydrogen Permeation in X65 Steel under Cyclic Loading’. Chan, K. S. (2010) ‘Roles of microstructure in fatigue crack initiation’, International Journal of Fatigue , 32(9), pp. 1428 – 1447. doi: 10.1016/j.ijfatigue.2009.10.005. Cheng, Y. W. (1985) ‘The fatigue crack growth of a ship steel in seawater under spectrum loading’, International Journal of Fatigue , 7(2), pp. 95 – 100. doi: 10.1016/0142-1123(85)90039-8. References